Auto Shift Manual Mode Circuit Intermittent
The P0959 code indicates an intermittent fault in the manual shift mode circuit of an automatic transmission. This circuit allows the driver to manually select gears via the shift lever or paddles. An intermittent signal suggests a loose connection, damaged wiring, or a failing sensor/switch, causing the transmission control module to lose communication with the manual mode input.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Inability to manually shift gears or erratic manual mode operation
- Transmission stuck in automatic mode or default gear
- Intermittent loss of manual shift function
2. Most Common Causes
- Loose or corroded electrical connections in the manual mode circuit
- Damaged, worn, or intermittently shorted wiring
- Faulty manual mode switch or sensor (internal wear)
- Intermittent transmission control module (TCM) failure
- Poor ground in the manual mode circuit
- Moisture or contamination in the shift lever switch connectors
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and record freeze frame data.
Step 2: Visually inspect the manual shift mode switch and wiring harness for damage, corrosion, or loose connections.
Step 3: Test the switch/sensor resistance and continuity per manufacturer specs.
Step 4: Check for intermittent shorts or opens by wiggling the harness while monitoring the circuit with a multimeter or oscilloscope.
Step 5: If wiring and switch are good, test the transmission control module for proper input/output signals.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with this code as it may cause unpredictable shifting, potentially leading to transmission damage or loss of control. Have it diagnosed promptly.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for diagnosis and repair, depending on the root cause (e.g., switch replacement vs. wiring repair).
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.